Calcined clays traditionally have been used as carriers for granular pesticides. Granular pesticides having a calcined clay carrier are limited because such carriers can accommodate no more than about 10% by weight of a pesticide. The amount of pesticide is limited because the pesticide merely enters the pore structure of the calcined clay. When the available sites in the pore structure are filled, then no further pesticide can be held by the calcined clay. If the available surface area of the carrier was greater, the amount of pesticide in a granular product could be increased up to about 30% to 40% by weight of the pesticide granule.
It also is well known that phyllosilicates, such as smectite clays, e.g., sodium montmorillonite and calcium montmorillonite, can be treated with organic molecules, such as organic ammonium ions, to intercalate organic molecules between adjacent, planar silicate layers, for bonding the organic molecules with a polymer to intercalate the polymer between the layers, thereby substantially increasing the interlayer (interlaminar) spacing between the adjacent silicate layers. The thus-treated, intercalated phyllosilicates, having interlayer spacings of at least about 10 .ANG. and up to about 100 .ANG., then can be exfoliated, i.e., the silicate layers are separated, e.g., mechanically, by high shear mixing. The individual silicate layers, when admixed with a matrix polymer, before, after or during the polymerization of the matrix polymer, e.g., a polyamide--see U.S. Pat. Nos. 4,739,007; 4,310,734; and 5,385,776--have been found to substantially improve one or more properties of the polymer, such as mechanical strength and/or high temperature characteristics.
Examples of such prior art composites, also called "nanocomposites," are disclosed in published PCT disclosure WO 93/04118 and U.S. Pat. No. 5,385,776, disclosing the admixture of individual platelet particles derived from intercalated layered silicate materials, with a polymer to form a polymer matrix having one or more properties of the matrix polymer improved by the addition of the exfoliated intercalate. As disclosed in WO 93/04118, the intercalate is formed (the interlayer spacing between adjacent silicate platelets is increased) by adsorption of a silane coupling agent or an onium cation, such as a quaternary ammonium compound, having a reactive group which is compatible with the matrix polymer. Such quaternary ammonium cations are well known to convert a highly hydrophilic clay, such as sodium or calcium montmorillonite, into an organophilic clay capable of sorbing organic molecules.
A publication that discloses direct intercalation (without solvent) of polystyrene and poly(ethylene oxide) in organically modified silicates is Richard A. Vaia et al., "Synthesis and Properties of Two-Dimensional Nanostructures by Direct Intercalation of Polymer Melts in Layered Silicates," Chem. Mater., 5:1694-1696 (1993). Also, as disclosed in Richard A. Vaia et al., "New Polymer Electrolyte Nano-composites: Melt Intercalation of Poly(Ethylene Oxide) in Mica-Type Silicates," Adv. Materials, 7, No. 2: (1985), pp. 154-156, poly(ethylene oxide) can be intercalated directly into sodium (Na) montmorillonite and lithium (Li) montmorillonite by heating to 80.degree. C. for 2-6 hours to achieve a d-spacing of 17.7 .ANG.. The intercalation is accompanied by displacing water molecules, disposed between the clay platelets, with polymer molecules. Apparently, however, the intercalated material could not be exfoliated and was tested in pellet form. It was quite surprising to one of the authors of these articles that exfoliated material could be manufactured in accordance with the present invention.
Previous attempts to intercalate polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA) and poly(ethylene oxide) (PEO) between montmorillonite clay platelets met with little success. As described in Levy et al., "Interlayer Adsorption of Polyvinylpyrrolidone on Montmorillonite," Journal of Colloid and Interface Science, Vol. 50, No. 3, March 1975, pages 442-450, attempts were made to sorb PVP (40,000 average M.W.) between monojonic montmorillonite clay platelets (Na, K (potassium), Ca (calcium), and Mg (magnesium)) by successive washes with absolute ethanol, and then attempting to sorb the PVP by contact with 1% PVP/ethanol/water solutions, with varying amounts of water (H.sub.2 O), via replacing the ethanol solvent molecules that were sorbed in washing (to expand the platelets to about 17.7 .ANG.). Only the sodium montmorillonite had expanded beyond a 20 .ANG. basal spacing (e.g., 26 .ANG. and 32 .ANG.), at 5.sup.+ % H.sub.2 O, after contact with the PVP/ethanol/H.sub.2 O solution. It was concluded that the ethanol was needed to initially increase the basal spacing for later sorption of PVP, and that water did not directly affect the sorption of PVP between the clay platelets (Table II, page 445), except for sodium montmorillonite. The sorption was time consuming and difficult and met with little success.
Further, as described in Greenland, "Adsorption of Polyvinyl Alcohols by Montmorillonite," Journal of Colloid Sciences, Vol. 18, pages 647-664 (1963), polyvinyl alcohols containing 12% residual acetyl groups could increase the basal spacing by only about 10 .ANG. due to the sorbed polyvinyl alcohol (PVA). As the concentration of polymer in the intercalant polymer-containing solution was increased from 0.25% to 4%, the amount of polymer sorbed was substantially reduced, indicating that sorption might only be effective at polymer concentrations in the intercalant polymer-containing composition on the order of 1% by weight polymer, or less. Such a dilute process for intercalation of polymer into layered materials would be exceptionally costly in drying the intercalated layered materials for separation of intercalate from the polymer carrier, e.g., water, and, therefore, apparently no further work was accomplished toward commercialization.
In accordance with one embodiment of the present invention, intercalates are prepared by contacting a phyllosilicate either with water, or with an aqueous solution of a water-soluble polymer and/or a water-miscible organic solvent, like an alcohol, followed by contact with a monomeric organic pesticide compound or a solution of a pesticide compound. Typically, the pesticide compound has a polar organic moiety, such as a carbonyl functionality, like, for example, a carboxylic acid, or salt thereof, an ester, an amide, an aldehyde, a ketone, or a mixture thereof. The pesticide also can contain other polar organic moieties in addition to, or in place of, the carbonyl functionality, such as, for example, a sulfur-oxygen moiety, a phosphorus-oxygen moiety, a cyano moiety, or a nitro moiety. If the intercalate is prepared using an aqueous solution of a water-soluble polymer and/or a water-miscible organic solvent, then nonpolar pesticides, like chlordane and lindane, can be intercalated between clay platelets.
The addition of a pesticide or pesticide solution displaces the water and water-soluble polymer, if present, disposed between the clay platelets of the intercalate. The pesticide, therefore, displaces the water and water-soluble polymer between the clay platelets. The intercalated pesticide then is dried to remove the water, and pelletized to provide a granular pesticide containing up to 40% by weight of a pesticide.
In accordance with an important feature of the present invention, best results are achieved by using an aqueous solution of a water-soluble polymer, like polyvinylalcohol, and/or a water-miscible organic solvent, to first intercalate, i.e., activate, the clay, then using an organic pesticide compound having at least one polar organic moiety, and preferably a carbonyl functionality, in a concentration of at least about 2%, preferably at least about 5%, more preferably at least about 10%, by weight, based on the weight of organic pesticide compound and carrier (e.g., water, an organic solvent for the pesticide compound, or a mixture thereof) to achieve better sorption of the organic pesticide compound between phyllosilicate platelets. If the pesticide is a solid at intercalating temperature, it can be dissolved in a solvent. If the pesticide is a liquid compound at intercalating temperature, the pesticide can be intercalated between phyllosilicate platelets without using a solvent.
Regardless of the concentration of organic pesticide compound in a solvent, a water-soluble polymer:layered material ratio of at least 1:20, preferably at least 1:10, more preferably at least 1:4, and most preferably about 1:2, by weight, achieves efficient intercalation of the organic pesticide compound between adjacent platelets of the layered material. A water-miscible organic solvent can be used in place of the water-soluble polymer. It has been theorized that water, or aqueous solution of water-soluble polymer, intercalates between the clay layers to activate the clay, then the organic pesticide compound displaces the water and water-soluble polymer and is bonded to the silicate platelets via chelation-type bonding with the exchangeable cation, or via electrostatic or dipole/dipole bonding. The sorption of the water and/or water-soluble polymer, causes separation or added spacing between adjacent silicate platelets. An extrusion process accelerates intercalation of the pesticide between activated clay platelets.
For simplicity of description, all organic pesticide compounds are hereinafter termed an "intercalant pesticide." The water-soluble polymers are hereinafter termed an "intercalant polymer." In this manner, the water-soluble polymers, and subsequently the organic pesticides, are sufficiently sorbed to increase the interlayer spacing of the phyllosilicate in the range of about 5 .ANG. to about 100 .ANG., preferably at least about 10 .ANG., for easier and more complete exfoliation, if desired, in a commercially viable process, regardless of the particular phyllosilicate or intercalant pesticide.
In accordance with the present invention, it has been found that a phyllosilicate, such as a smectite clay, that has been activated with water or an aqueous solution of a water-soluble polymer and/or a water-miscible organic solvent, can be intercalated by sorption of organic pesticide compounds having a polar moiety, like carbonyl functionality, to provide bonding of the polar moiety to the internal surfaces of the layered material by a mechanism selected from the group consisting of ionic complexing, electrostatic completing, chelation, hydrogen bonding, dipole/dipole interaction, Van Der Waals forces, and any combination thereof. Such bonding between the polar moieties of one or two intercalant pesticide molecules and the metal cations bonded to the inner surfaces of the phyllosilicate platelets provides adherence between the organic pesticide molecules and the platelet inner surfaces of the layered material. Activation of the clay and sorption and bonding of a platelet metal cation between two electronegative atoms of the intercalant pesticide molecules, like oxygen, sulfur, or nitrogen, for example, increases the interlayer spacing between adjacent silicate platelets or other layered material to at least about 5 .ANG., preferably to at least about 10 .ANG., and more preferably at least about 20 .ANG., and most preferably in the range of about 30 .ANG. to about 100 .ANG.. In addition, if a water-soluble polymer is used to activate the phyllosilicate, the intercalant polymer provides sufficient interlayer spacing such that pesticides lacking a polar group can be intercalated into the clay.
The intercalated clay containing a pesticide, i.e., intercalated pesticide product, can be used directly as a pesticide product. The intercalated pesticide also can be used as the active ingredient in a granular, dust, or wettable powder pesticide composition by admixture of the solid pesticide intercalant with ingredients well known in the art.
Such intercalated pesticides also easily can be exfoliated, if desired, into individual phyllosilicate platelets before or during admixture with a liquid carrier or solvent, for example, one or more monohydric alcohols, such as methanol, ethanol, propanol, and/or butanol, polyhydric alcohols, such as glycerols and glycols, e.g., ethylene glycol, propylene glycol, butylene glycol, glycerine, and mixtures thereof, aldehydes, ketones, carboxylic acid esters, amines, hydroxyethers, like ethylene glycol monobutyl ether, glycol ether esters, like cellosolve acetate, aromatic or aliphatic hydrocarbons, and other organic solvents, like DMSO, DMF, or HMPA. The exfoliated platelets can be used for delivery of any active hydrophobic or hydrophilic organic pesticide compound, such as a contact or a systemic pesticide compound, dissolved or dispersed in the carrier or solvent to provide either a solid, as a granular, dust, or wettable powder, or a thixotropic composition.